The use of natural gas as a fuel for internal combustions engines is increasing because of its low cost, availability, and clean burning characteristics. Current storage methods based on liquefied, compressed, and adsorbed natural gas require a storage vessel or tank to be supplied with gas at elevated pressures. In the case of liquefied natural gas a compressor is used to cool and liquefy gas by adiabatic expansion. In the case of compressed natural gas, a mechanical compressor is used to increase the pressure in the storage vessel to tens of MPa. Gas is also compressed to fill adsorbed natural gas tanks at pressures between about 3 MPa and about 25 MPa.
A problem with current methods of filling natural gas tanks is that pressurizing flammable natural gas is hazardous and requires mechanical compressors with multiple stages to prevent thermal decomposition of the gas. Filling an absorbed natural gas tank generates heat from compression of the gas, friction between moving pump parts, and, through the enthalpy of adsorption, from binding of the gas to the sorbent. Therefore, a second problem with current methods of filling adsorbed natural gas tanks is management of heat produced by compression and adsorption. Thus, there exists a need for improved systems and methods for filling and storing tanks with natural gas.